JP2017532607A - Optical assembly and method of manufacturing optical assembly - Google Patents

Abstract

The present invention relates to an optical assembly and a method of manufacturing the optical assembly. The invention also relates to the use of an optical assembly. Laser radiation received through a bundle of individual light supply fibers is directed to a fiber laser fiber. Each feed fiber has a cladding layer that surrounds the core of the fiber and provides total internal reflection within the core, and the fiber cladding layer is at least partially melted to form a zone that is within the zone. Including a fiber core disposed in a cylindrical configuration. With this configuration, formation of an annular laser beam that can be supplied to a fiber laser fiber having an annular light guiding zone is provided, and the annular laser beam can be provided to a workpiece, for example. [Selection] Figure 2

Description

  The present invention relates to fiber optic components, and more particularly to adiabatic optical fiber couplers and uses thereof. The invention also relates to an optical fiber focusing method for the production of fiber optic components. The present invention is particularly suitable for material processing using high-power laser light.

  High-power laser light is widely used for material processing such as metal cutting and welding. The processing speed using laser light varies depending on the characteristics of the laser light itself such as wavelength, beam quality, and beam profile as well as various material characteristics such as material composition and thickness. Particularly in metal cutting applications, the beam profile, ie the spatial intensity pattern of light, has been considered to affect the cutting speed and quality. The typical profile of the laser light can be approximated by either a Gaussian (bell) shape or a super Gaussian shape. The Gaussian distribution is generated by a single mode laser source, while the super Gaussian shape is generated by a multimode laser. An extreme example of a Super Gaussian shape is a so-called top hat shape, where the intensity inside the beam is constant and the intensity outside the beam is zero. A common feature of Gaussian and top hat beams is that a significant amount of intensity exists in the center of the beam.

  When a metal is cut with a laser beam, the laser beam is typically focused on a spot of 100 to 500 μm by a condenser lens to increase the energy density, and the workpiece is instantaneously heated to a metal melting point of 1500 ° C. or higher. To melt or sublimate. At the same time, an assist gas may be supplied to remove the melt and cut the workpiece. When the workpiece is a thick mild steel plate (carbon steel plate), oxygen is used as an assist gas to generate heat of oxidation reaction, and the workpiece is cut using the heat.

  Laser light of 1 micrometer wave band from a solid state laser or fiber laser realizes a very high light energy intensity and absorbance on a metal workpiece as compared with laser light of 10 micrometer wave band from a CO2 laser.

  However, when a 1-micrometer wave band laser beam of a Gaussian beam is used together with an oxygen assist gas to cut a mild steel plate workpiece, the melting width of the upper surface of the workpiece is unnecessarily widened and cutting kerf control is impaired. In addition, self-combustion can occur, degrading the quality of laser cutting. However, in European Patent Application No. 2762263 (Patent Document 1), it has been found that if the laser beam of a fiber laser is formed in a ring beam shape and the workpiece is cut with this ring beam, the same effect as cutting with a CO2 laser can be obtained. Yes.

  Certainly, metal cutting with laser light having an intensity profile that can be approximated in an annular or “doughnut” shape has yielded good results in terms of cutting speed and quality. For example, it has been thought that cutting a metal of a given thickness can be done with a much lower power when using a donut-shaped beam instead of a conventional beam profile. Accordingly, some companies that manufacture high power laser sources for such applications have developed methods for generating beam profiles that approximate or approximate a donut shape. Some of these methods include using a laser resonator ring mode, such as the transverse (TEM) mode, or shaping the beam using sophisticated and often patented electro-optic methods. In a donut-shaped beam, the intensity profile has a relatively dark depression or region at the center of the beam, and the region of maximum radiation intensity forms a ring-shaped pattern around the central depression.

  US Patent Publication No. 20110293215 discloses a means for converting a Gaussian mode beam into an annular mode beam using a hollow optical fiber or a fiber coupled microaxicon lens assembly.

  From JP 2013-139039 A (Patent Document 3), it is known that a plurality of optical fibers are directed to a corresponding number of collimating lenses, and laser beams from two or more optical fibers are made parallel. This means has a condensing lens that collects the parallel light from the collimating lens, while the optical fiber is moved by a drive mechanism to produce an annular beam in several shapes.

  U.S. Pat. No. 7,348,517 (Patent Document 4) describes a problem of removing a workpiece melt when, for example, a steel plate is cut with a laser beam. An assist gas such as oxygen or an inert welding gas is injected coaxially with the laser beam so that the melt is removed locally. If an appropriate gas pressure is maintained with a thick plate, the power to blow off the molten metal tends to be insufficient. The TEM10 mode is used to generate the annular beam, and this focusing is optimized by modifying the configuration of the gas laser oscillator and / or modifying the configuration of the optical mirror and lens system used.

  European Patent Application No. 0464213 (Patent Document 5) cuts a workpiece mainly with a ring mode laser beam and cools the system by applying a gas to the surface of the optical system, thereby laser beaming a thick plate workpiece such as mild steel. Discloses a method of cutting with a. A KCL (potassium chloride) lens is used as the focusing lens.

  Finally, International Publication No. 2009003484 (Patent Document 6) combines a first optical segment made of a focused optical fiber with a second segment having a waveguide including an inner clad, so that the light enters a ring-shaped region. An adiabatic optical coupler adapted to be guided is disclosed. In order to confine light in the ring-shaped guiding region, the inner cladding has a low refractive index relative to undoped silica.

  In material processing applications using laser light, it is generally preferable to maximize the brightness of the beam. Brightness is defined as the output per unit solid angle and unit area. As an example of the importance of brightness, increasing the brightness of the laser light means that the laser light can be used to increase the processing speed or material thickness. Thus, to maximize the brightness of the light emitted by the fiber optic bundle, the fiber cores must be as close together as practicable.

  For example, when a large number of optical fibers having a cladding diameter of 125 μm and a core diameter of 20 μm are focused, high brightness cannot be obtained because the fiber cores are relatively far apart in the bundle. If it is desired to increase the brightness of the focus, it is necessary to reduce the spacing between the cores in the fiber. Prior art measures do not adequately address this problem. Brightness lost due to too large a fiber or a break or deviation in the optical path cannot be recovered.

European Patent Application No. 2762263 US Patent Application Publication No. 20110293215 Japanese Unexamined Patent Publication No. 2013-139039 US Pat. No. 7,348,517 European Patent Application No. 0464213 International Publication No. 2009003484

  An object of the present invention is to realize a robust method for generating an annular or ring-shaped laser radiation pattern with very high brightness and luminous intensity. Such a ring-shaped intensity distribution pattern can be immediately applied industrially in material processing using laser light.

  The object of the invention is achieved by an optical assembly and method as set out in the independent claims.

  Inventive optical assemblies and methods relate specifically to fiber optic components operating in the 100 W to kW power range. In particular, the throughput of this component can be at least 100 W, in particular at least 1 kW. The component supply fiber may be a fiber laser or any other fiber delivery laser source or may be coupled thereto. A sufficient amount of brightness is maintained by using thin fibers, melting the fiber cladding, eliminating or at least minimizing disturbances or misalignments in the optical path. In this way, the fiber cores are brought close to each other according to the core diameter.

  According to one aspect of the invention, an optical assembly is provided that directs laser radiation received through a bundle of individual light delivery fibers. Each feed fiber has at least one cladding layer surrounding the fiber core. According to the present invention, the cladding layer of the fiber is at least partially melted into a cylindrical confinement to form a zone, which zone is at least of a supply fiber arranged in a cylindrical configuration within this zone. Includes some cores. This provides an annular light guide, whereby the laser light is supplied to a fiber laser fiber, for example in a “donut” shape. The present invention can be used in any type of fiber laser device where the intensity pattern of the laser radiation needs to have an annular shape.

  In one embodiment, the bundles of individual light delivery fibers are melted to form a tubular zone that includes a core of delivery fibers arranged in a cylindrical configuration within the zone. Also, the bundle of individual light supply fibers has a further optical fiber melted in the center of the annular zone, which makes it possible to provide laser light also in the center of the annular laser light. This central fiber may be a dummy or unused fiber whose sole task is to help maintain the position of the supply fiber along the periphery of the tubular mold in which the fiber is melted. .

According to one aspect of the invention, a method is provided for manufacturing an optical assembly that directs laser radiation received through a bundle of individual light delivery fibers to a fiber laser fiber. This inventive method
-Providing a cylindrical mold;
-In the mold described above, the step of fitting a plurality of light supply fibers along a cylindrical circumference, each fiber surrounding the core and at least one cladding surrounding the core and providing total internal reflection in the core A step having a layer;
-The cladding material of the above-mentioned fiber in the above-mentioned mold is heated and at least partially melted, and at least a part of the core of the above-mentioned supply fiber is arranged in a cylindrical configuration in the molten cladding material Forming a zone.

  According to an embodiment, in the melting step, the cladding material of the fiber described above is melted to form an annular zone, the zone comprising the core of the supply fiber described above arranged in a cylindrical configuration within the zone. . Additional optical fiber may be melted in the center of the annular zone.

  Preferably, the melting step is performed by using a tubular mold having an inner diameter forming a waist portion and applying heat to melt the fiber bundle of the waist portion. The spacing between the cores of the supply fiber is relatively small because it melts with the fiber bundle. Thus, the molten portion of the fiber bundle can form a single glass or at least a compact zone of the molten fiber cladding.

  The annular laser light produced by the inventive optical assembly is fed into a fiber having a core capable of directing laser radiation. The core of the feed fiber is advantageously arranged in an annular zone or region of a predetermined size that overlaps the tubular core region of the donut-shaped fiber laser fiber. Such a core region has a higher refractive index than the surrounding material and provides total internal reflection to the core region. Various embodiments are defined in the dependent claims. If the annular zone has a higher refractive index than the material surrounded by the annular zone and the material outside this, the laser light is directed to the workpiece, which can be, for example, degraded annular strength profile and optical power and intensity. Cutting with minimal attenuation.

  In summary, the method described above is a simple and efficient way of generating a “ring-shaped” beam profile for a fiber coupled laser source. In the preferred method of joining the first and second optical elements, free space optical communication is not required. Complex electromechanical and electro-optic systems are not used. A single-mode or multi-mode laser light source can be used for incidence, and unlike some publicly available ring generators, the resonator characteristics of the laser light source need to be changed to generate a ring-shaped intensity distribution There is no.

  Significant advantages are obtained by the means of the present invention. Since this component is preferably an all-glass component that has been melted, there is no alignment error or destruction effect due to contamination. Since this component is stable over time and environmental changes, the quality of material processing is not affected by these. Certain advantages are gained in components directed to or used in laser welding and laser cutting.

  Next, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

1 is a cross-sectional view of an optical fiber bundle or preform. FIG. 4 shows a melted bundle forming an optical assembly according to an embodiment of the invention. It is a figure which shows the structure and refractive characteristic of an annular fiber laser fiber. It is a figure which shows the structure and refractive characteristic of an annular fiber laser fiber. It is a figure which shows the tubular casting apparatus by one Embodiment of this invention. It is a figure which shows the tubular casting apparatus by another embodiment of this invention. FIG. 4 shows a fused bundle of input fibers according to one embodiment of the present invention. FIG. 3 shows a coupling zone between an inventive optical assembly and a fiber laser fiber.

  FIG. 1 is a cross-sectional view of a bundle 10 of optical fibers 11 constituting a preform of an optical element according to an embodiment of the present invention. The bundle has N fibers (where N = 4). Each fiber 11 has a core 12 and a cladding 13. The clad is made of a material having a refractive index lower than that of the core 12. As is well known to those skilled in the art, light incident on the core of such a fiber (also referred to as a step index fiber) is guided by a refractive index step between the core and the cladding and follows the principle of total internal reflection. Stay within.

  In order to maximize the brightness of the optical pattern formed by the multiple cores, the bundle fiber according to the invention is very thin. In particular, the fiber diameter may be 40 μm or less. Since handling and focusing of such thin fibers is very difficult, the bundle is preferably melted in a supporting cylindrical mold to increase manufacturability.

  FIG. 2 shows a melt bundle 20 forming an optical assembly according to one embodiment of the present invention. The melt bundle 20 is generated by first forming a focused fiber preform 10 as shown in FIG. 1 and then withdrawing the preformed bundle from a heated cylindrical mold of capillaries. . As it passes through the mold, the cladding 23 of the fiber 21 is controlled and melted. The spatial pattern formed by the core 22 is determined by the preform and the mold. In this case, the melt bundle has N core regions 22 (N = 4 in this case). The cladding region 23 and possibly the core region 22 are also deformed from their initial generally round shape by a melting process. The dotted lines in FIG. 2 show the approximate deformation boundaries of the individual fibers 11 in the bundle of FIG. Such a physical interface can disappear in the melting process.

  The final physical dimensions and spatial separation of the core of the melt bundle 20 are determined by the fiber dimensions and the degree of melting of the cladding. The outer layer 24 is constituted by a tubular mold. Thus, the capillary is melted with the fiber to form a solid portion of glass. This provides a molten fiber bundle with high mechanical robustness and melts the fiber bundle and capillary tube to form a solid solid glass piece. Alternatively, if the mold is not part of the structure, any suitable cladding can be formed on the melted fiber. The formed fiber bundle 20 may be polished or cleaved in a conventional manner to form a flat end or interface surface, and the addition or stripping of an external protective polymer coating using conventional fiber optic methods. The resulting fiber may be further processed.

  FIG. 3a shows a fiber laser fiber 30 having an annular light guide (donut-like fiber) that receives the laser light output from the molten fiber bundle of FIG. The donut-shaped fiber 30 has a central clad 34, an annular light guide or core 31, a primary clad 32, and a secondary clad 33. The doughnut-shaped fiber 30 may be polished or cleaved using a well-known method of fiber optics to form a flat surface.

  The molten fiber bundle 20 and the doughnut-shaped fiber 30 may be optically coupled by either bonding or free space optical communication (such as a lens). Laser radiation that is optically coupled from the core of the supply fiber 21 to the core 31 of the doughnut-shaped fiber forms a spatial intensity distribution that can approximate a donut shape at the output face of the donut-shaped fiber. This spatial intensity pattern can be further imaged on the workpiece by the machining optical system.

FIG. 3b shows a possible refractive index profile of the donut fiber 30 of FIG. 3a. The central cladding 34 has a refractive index of n _{4 and} the primary cladding 32 has a refractive index of n ₂ . The refractive index of the core 31 is n ₁ , and n ₁ > n ₂ and n ₁ > n ₄ so that light enters the core 31 and remains guided. The refractive index n ₃ of the secondary cladding is not explicitly limited in size, but in practice this region is typically composed of pure fused silica, so n ₃ can be about 1.45. The refractive index of fused silica can be adjusted by doping impurities. For example, when the fused silica is doped with germanium, the refractive index is increased, and when doped with fluorine, the refractive index is decreased. Therefore, the core 31 of the donut-shaped fiber may be made of fused silica doped with germanium, and the primary clad 32 may be made of fused silica doped with fluorine. The central clad 34 and the secondary clad 33 may be composed of undoped fused silica.

Of course, other material choices that meet the requirements for refractive index values in different regions of the fiber 30 are possible. Since some of the light is also incident on the central cladding 34, the refractive index of the primary cladding n ₂ is made smaller than the refractive index n _{4 of} the central cladding, and the light incident on the central cladding 34 is surely incident on the primary cladding 32 It is also possible not to propagate to.

  Referring to FIG. 4a, according to one embodiment, the tubular casting apparatus is used to obtain a waist portion 43 of a suitable length (eg, 1 mm to 5 cm, preferably 3 mm to 3 cm) with a substantially constant diameter. It has a capillary tube 42 (for example, fused silica, quartz, doped quartz, etc.) that is tapered by a glass stretching method. A bundle 40 of supply fibers 41 is fitted in a capillary tube 42. The inner diameter of the capillary tube 42 in the waist portion 43 is configured to be slightly larger than the outer diameter of the bundle 40 of the supply fibers 41 by, for example, about 1 μm. The bundle 40 may be compacted by a suitable focusing aid, and the bundle geometry may be secured by a supply fiber having an adhesive coating (not shown) or the like.

  Within the capillary waist 43, the bundle of supply fibers 41 is melted with the walls of the capillary 42, for example by applying heat to the heating zone 44, and preferably adiabatic (gradual) melting of the fibers. As a result, a molten fiber bundle 45 is obtained.

  FIG. 4 b shows an alternative embodiment, where the tubular mold 46 with the waist 47 does not form part of the molten fiber bundle 48. Both of the embodiments of FIGS. 4a and 4b perform an important feature of the present invention, i.e., a very gentle manufacturing step on the fiber bundle being melted, and adiabatic light transmission throughout the optical assembly. It shows that induction is maintained. In practice this means avoiding as much as possible deformation, bending and disturbance of the fiber core.

  In general, due to the associated geometry, the cross section of the fiber core is such that the bundle of fibers and capillaries are melted and the air pockets between the fibers and between the fibers and the inner wall of the cylindrical mold are melting. As it disappears due to glass reflow, it changes from a circular shape to a non-circular shape. The fiber shape change must be made progressively (adiabatic) along the length of the melted region. A gradual shape change controls the heating power of a heating zone, such as zone 44 shown in FIGS. 4a and 4b, or keeps the heat source constant as the fiber moves at a constant speed along the elongated melt zone. Can be achieved by a combination of these heating powers or a combination thereof. The minimum heating power is such that the core of the supply fiber 41 remains in its original shape and the capillary tube (or mold) is not substantially destroyed. The gradual change of the core shape is indispensable to keep the loss and decrease in brightness of laser radiation low.

  FIG. 5 is a cross-sectional view of an embodiment of the invention that uses a molten fiber bundle 50 having seven feed fibers. In this dense configuration of feed fibers, one of the fibers is placed in the center of the bundle and the remaining six fibers are arranged in a cylindrical shape and appear in a circularly arranged cross section. The surrounding fiber has a core 51 and the center fiber has a core 52. The solid glass matrix 53 is composed of seven individual feed fiber claddings, capillaries and / or other claddings applied around the original fiber bundle.

  FIG. 6 shows the optical interface between the melted bundle 50 of FIG. 5 and the donut fiber 30 of FIG. 3a. For the sake of clarity, the dotted line is drawn from the sign to indicate the structure represented by the dotted line. The core 51 of the supply fiber, which is arranged in a ring and is now melted, is aligned so that the optical power is incident on the core 31 of the donut fiber 30. Accordingly, the core of the center fiber 52 of the melt bundle 50 is configured so that the optical power is incident on the center clad 34 of the doughnut-shaped fiber 30. Therefore, the luminous intensity at the center of the doughnut-shaped fiber 30 does not become zero if the optical power is incident on all the fibers of the melt bundle 50.

The dimensions of the melt bundle 50 and the doughnut-shaped fiber 30 may be selected so that the surrounding fiber 51 overlaps the central cladding 34 of the donut-shaped fiber 30 because in some cases the optical power from the core 51 is also somewhat centered. This is because it is preferably incident on the clad 34. The optical power incident on the central cladding 34 does not continue to be constrained by the cladding because the refractive index n ₄ is less than the refractive index n ₁ of the core 31.

  On the other hand, when the overlap between the cores is 100%, that is, when all the cores 51 of the fiber bundle 50 are fitted inside the core 31 of the doughnut-shaped fiber 30 and the core 52 is kept essentially dark, Is not incident on the central cladding 34. Thus, the central cladding 34 also appears dark, i.e., the light intensity is actually zero.

Thus, the spatial configuration and dimensions of the core regions of optical elements 30 and 50 define a complete overlap of the cores. In most cases, it is preferred not to enter power into the primary cladding 32 because this light is not contained in the core 31 and the central cladding 34 and can therefore be considered an undesirable loss for the component. This is especially true in the case of n ₃ > n ₂ , which is an important practical case. In this case, any light incident on the primary cladding 32 leaks into the secondary cladding 33.

  It should be understood that embodiments of the disclosed invention are not limited to the specific structures, process steps, or materials disclosed herein, but are extended to equivalents thereof as would be recognized by one skilled in the art. . It is also to be understood that the terminology used herein is used for the purpose of describing particular embodiments only and is not intended to be limiting.

  References herein to “one embodiment” or “an embodiment” refer to a particular feature, structure, or characteristic described in connection with the embodiment, that is at least It is meant to be included in one embodiment. Accordingly, the phrases “one embodiment” or “an embodiment” described at various places in the specification are not necessarily all referring to the same embodiment. .

  Various embodiments and examples of the invention may be referred to herein, along with alternatives to their various components. It will be understood that such embodiments, examples and alternatives should not be construed as substantially equivalent to each other and should be regarded as an independent and autonomous representation of the invention.

  Furthermore, the described features, structures, or characteristics may be combined into one or more embodiments by any suitable method. In this specification, a number of specific details, such as examples of length, width, shape, etc., have been provided to provide a thorough understanding of embodiments in the present invention. However, one of ordinary skill in the art appreciates that the invention can be practiced without one or more specific details, or with other methods and structures. In other instances, well-known structures or operations are not shown in detail in order to avoid obscuring the description of the embodiments.

  While the above examples illustrate the principles of the present invention in one or more specific applications, those skilled in the art will appreciate that many changes in the embodiments, usage and details can be found in the invention. It will be apparent that this can be done without exercising and without departing from the principles and concepts of the present invention. Accordingly, the invention is not intended to be limited except as by the claims set forth below.

Claims (8)

  An optical assembly for directing laser radiation received through a bundle of individual light supply fibers, each supply fiber having at least one cladding layer surrounding the core of the fiber and providing total internal reflection within the core. Providing the cladding layer of the fiber at least partially melted into a cylindrical confinement to form a zone, the zone of the supply fiber disposed in a cylindrical configuration within the zone; An optical assembly comprising at least a portion of a core and providing an annular light guide.   2. An optical assembly according to claim 1, wherein a bundle of individual light supply fibers is melted to form an annular zone comprising a core of supply fibers arranged in a cylindrical configuration of the zone. .   3. The optical assembly according to claim 2, wherein the bundle of individual light delivery fibers includes a further optical fiber melted at the center of the annular zone, providing a light guide at the center of the annular light guide. Optical assembly characterized. A method of manufacturing an optical assembly that directs laser radiation received by a bundle of individual light delivery fibers, comprising:
-Providing a cylindrical mold;
-Fitting a plurality of light delivery fibers along a cylindrical circumference in the mold, each fiber surrounding the core and at least one cladding layer providing total internal reflection in the core A step comprising:
-Applying a heat to the fiber cladding material in the mold to at least partially melt and providing a zone in which at least a portion of the core of the supply fiber is arranged in a cylindrical configuration within the molten cladding material; Forming the method.   5. The method of claim 4, wherein the fiber cladding material is melted to form an annular zone, the annular zone comprising a core of the feed fiber disposed in a cylindrical configuration of the zone. And how to.   6. The method of claim 5, further comprising melting an optical fiber at the center of the annular zone.   The method according to any one of claims 4 to 6, wherein a tubular mold having an inner diameter forming a waist portion is used as the cylindrical mold, and heat is applied to bundle the bundle of fibers at the waist portion. A method characterized by melting.   Use of an optical assembly according to any one of claims 1 to 3 for generating an annular laser beam and guiding it in a fiber laser fiber having a cross section in an annular zone. Use at least partly overlapping the laser beam and having a higher refractive index than the material surrounded by the annular zone and the material outside the annular zone.

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